Allow devices to inform the PCL interpreter that it must not alter palettes

Bug #692786 "Problem with HPGL paletted colour"

pdfwrite (and potentially other devices) can't cope with situations where the
interpreter alters the 'palette' (the lookup table in a /Indexed space) after
the space has been set to be the current color space.

However, if we unilaterally preserve the palette, it seems that this causes
performance problems (see bug #692786.

Here we add a new special op 'needs_invariant_palette' which allows a device
to communicate this. We alter the PCL interpreter to inquire the device's
requirements, and aler pdfwrite to communicate its needs.

This results in > 300 differences with pdfwrite, all of them progressions

4 files changed, 21 insertions, 0 deletions

diff --git a/gs/base/gdevdflt.c b/gs/base/gdevdflt.c
index 057264b14..375580ce6 100644
--- a/gs/base/gdevdflt.c
+++ b/gs/base/gdevdflt.c
@@ -929,6 +929,7 @@ gx_default_dev_spec_op(gx_device *pdev, int dev_spec_op, void *data, int size)
         case gxdso_is_native_planar:
         case gxdso_supports_devn:
         case gxdso_supports_hlcolor:
+        case gxdso_needs_invariant_palette:
             return 0;
         case gxdso_pattern_shfill_doesnt_need_path:
             return (pdev->procs.fill_path == gx_default_fill_path);
diff --git a/gs/base/gxdevsop.h b/gs/base/gxdevsop.h
index 61249b91a..da198a767 100644
--- a/gs/base/gxdevsop.h
+++ b/gs/base/gxdevsop.h
@@ -253,6 +253,14 @@ enum {
      * Return 0 for 'no special treatment', or 1 for the anitdropout
      * downscaler. */
     gxdso_interpolate_antidropout,
+    /* gxdso_needs_invariant_palette:
+     * The PCL interpreter can set a /Indexed coluor space, and then
+     * alter the palette afterwards. For rendering the paletter lookup
+     * is done as required, so this works, but for high level devices
+     * (eg pdfwrite) we can't deal with this. return '0' if the device
+     * doesn't care if the palette changes, and 1 if it does.
+     */
+     gxdso_needs_invariant_palette,
     /* Add new gxdso_ keys above this. */
     gxdso_pattern__LAST
 };
diff --git a/gs/devices/vector/gdevpdfi.c b/gs/devices/vector/gdevpdfi.c
index 5b16c6ad2..3e022c9a5 100644
--- a/gs/devices/vector/gdevpdfi.c
+++ b/gs/devices/vector/gdevpdfi.c
@@ -2530,6 +2530,11 @@ gdev_pdf_dev_spec_op(gx_device *pdev1, int dev_spec_op, void *data, int size)
                which is actually a devn vs. the pattern type for pdfwrite.
                We use this to distingush between the two */
             return 1;
+        case gxdso_needs_invariant_palette:
+            /* Indicates that it is not permissible to change /Indexed colour space
+             * palette entries after the colour space has been set.
+             */
+            return 1;
     }
     return gx_default_dev_spec_op(pdev1, dev_spec_op, data, size);
 }
diff --git a/pcl/pcpalet.c b/pcl/pcpalet.c
index 571d28f71..9a0066522 100644
--- a/pcl/pcpalet.c
+++ b/pcl/pcpalet.c
@@ -27,6 +27,7 @@
 #include "gxcmap.h"
 #include "gxdcconv.h"
 #include "gzstate.h"
+#include "gxdevsop.h"  /* for special ops */
 
 /* RC routines */
 gs_private_st_simple(st_palette_t, pcl_palette_t, "pcl palette object");
@@ -448,6 +449,12 @@ pcl_palette_set_color(pcl_state_t * pcs, int indx, const float comps[3]
         code = pcl_cs_indexed_set_palette_entry(&(pcs->ppalet->pindexed),
                                                 indx, comps);
 
+    /* Check if the device requires that the palette must not change */
+    if (dev_proc(pcs->pgs->device, dev_spec_op)(pcs->pgs->device,
+                                gxdso_needs_invariant_palette, 0, 0))
+        /* change the ID if so to indicate a difdferent colour space */
+        pcs->ppalet->pindexed->pcspace->id = gs_next_ids(pcs->memory, 1);
+
     if (pcs->monochrome_mode == 0) {
         was_gray = pcs->ppalet->pht->is_gray_render_method;